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R48258 — Carbon Dioxide Removal (CDR): Its Potential Role in Climate Change Mitigation

Reports · published 2024-11-12 · v2 · Active · crsreports.congress.gov ↗

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Authors
Jonathan D. Haskett
Report id
R48258
Summary

Rising global temperatures are associated with increasingly frequent and intense climate change impacts. Scientific consensus finds that stabilizing global temperatures is necessary to avoid increased climate impacts. Studies suggest that such stabilization requires human-caused carbon dioxide (CO2) emissions to be balanced by CO2 removals from the atmosphere, a condition known as net-zero carbon dioxide (CO2) emissions. While reductions in human-caused emissions of CO2 would be necessary to stabilize global temperatures, they may not be sufficient. This is due in part to the difficulty in eliminating emissions from some key economic sectors that are harder to decarbonize, including the steel and cement industries. These emissions are likely to persist after a program of emissions reductions and are known as residual emissions. Methods of further removing CO2 from the atmosphere may be necessary to counterbalance residual emissions. Researchers are enhancing nature-based techniques for increasing the uptake of CO2 from the atmosphere by the land surface and oceans, known as carbon sinks, as well as with recently developed technological methods. These are known collectively as carbon dioxide removal (CDR). Almost all the climate scenarios assessed by the Intergovernmental Panel on Climate Change that met specific global temperature stabilization levels used CDR to remove more CO2 from the atmosphere than is being added by emissions. CO2 is not the only greenhouse gas (GHG) with a climate effect. The influence of GHGs on global temperatures is the combined effect of CO2 and the other non-CO2 GHGs. Human-caused emissions of other GHGs—including methane (CH4), nitrous oxide (N2O), and hydrofluorocarbons (HFCs)—also increase global temperatures. No commercially available method for removing non-CO2 GHGs from the atmosphere exists. Therefore, to balance emissions of non-CO2 GHGs that cannot be abated, additional removals of CO2 from the atmosphere would be needed. There are several types and categories of CDR. Some CDR methods increase the uptake of CO2 on land by increasing forested area or increasing carbon sequestered in soils. Other methods have been proposed that increase the uptake of CO2 by the oceans through biological or chemical methods. A third category of CDR uses engineering methods such as chemically capturing CO2 from the air or from the combustion of biofuel energy crops and storing it in geological formations. Although almost all climate scenarios find that CDR would be necessary to meet global temperature goals, some researchers have raised concerns about relying on CDR to stabilize global temperatures. These concerns include uncertainties about the effectiveness, feasibility, and side effects of the deployment of certain CDR approaches at a scale necessary for such stabilization. For example, with CDR using forestry or soil carbon enrichment, there is concern that carbon could return to the atmosphere through forest fires or changes in tillage practices. As another example, for forestry and biofuel CDR, there is concern that the land area needed could impinge on food production. The possible ecological side effects of enhancing ocean uptake of CO2 have also caused concern. At the same time, researchers have noted potential co-benefits associated with certain CDR approaches, including improved crop production through increased levels of soil organic matter and reductions in ocean acidification through changes in ocean alkalinity. Laws enacted in the 117th Congress included funding for federal CDR research and development. For example, the 117th Congress passed the Infrastructure Investment and Jobs Act (IIJA; P.L. 117-58), the CHIPS Act of 2022 (P.L. 117-167), and the measure commonly known as the Inflation Reduction Act of 2022 (IRA; P.L. 117-169). Legislation to support the research, development, and implementation of CDR has been introduced in the 118th Congress. As the CDR programs and provisions supported by enacted legislation are implemented under congressional oversight, Congress may consider the future direction of federal CDR policy.

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